The present invention relates to an ink-jet printing apparatus and a print timing setting method for the apparatus, and more particularly, to print timing setting for an ink-jet printing apparatus which performs printing by scanning a carriage incorporating a printhead discharging ink relative to a print medium and which comprises an encoder outputting a detection signal in accordance with a predetermined distance of a carriage movement in a carriage scanning direction.
As a data output apparatus employed in, for instance, word processors, personal computers, facsimiles or the like, printers printing desired information, such as characters and images, on a sheet-type print medium, e.g., paper, film or the like, are widely used.
For a printing method of such printers, various printing methods are known. Particularly, an ink-jet printing method recently receives attention because of its capability to perform printing without contacting a print medium such as paper, ease of color printing, and quiet printing operation. In general, such printers widely adopt a serial printing method because of its low cost and ease of downsizing. According to the serial printing method, printing is realized by reciprocally scanning a carriage, incorporating a printhead discharging ink in accordance with desired print data, in the direction orthogonal to the conveyance direction of a print medium such as paper.
Furthermore, recently a printing method called a reciprocal printing or bi-directional printing is adopted to improve printing speed. According to this method, printing is realized by discharging ink from a printhead in both forward and backward directions of a carriage movement relative to a print medium.
FIG. 3 is a view showing a relation between printhead moving speed (scanning speed) and an ink droplet landing position. Described hereinafter is a case where a printhead 301, incorporated in a carriage (not shown), moves in the direction A in FIG. 3 at reference speed V. The distance between the printhead 301 and print medium 305 is d. When the printhead 301 discharges an ink droplet 303 at the position 307 onto the print medium 305 at discharge speed Vd, the ink droplet 303 travels at speed and the direction represented by composite vectors of the reference speed V and discharge speed Vd. The landing position of the ink droplet 303 on the print medium 305 is a position 306, which is deviated in the direction A by a distance xcex4 from the position 307 where the printhead 301 has actually discharged the ink droplet 303.
Assuming that the forward scan of the printhead 301 is the direction A, the backward scan of the printhead 301 is the direction B in a case of performing reciprocal printing. If the printhead 301 discharges ink in the backward scan at the same position as the position 307 where the ink droplet 303 is discharged in the forward scan, the ink droplet 303 lands on a position 310 which is deviated by a distance xcex4 in the direction opposite to the landing position 306 with respect to the position 307. As a result, even if an ink droplet is discharged at the same position in the forward and backward scans, the landing position on the print medium deviates by the distance from 306 to 310, i.e., 2xc3x97xcex4.
In order to eliminate the landing position deviation between the forward and backward scans, the ink-jet printing apparatus performs registration adjustment in reciprocal printing, making use of the fact that an ink droplet is normally discharged in a region where a printhead moves at constant speed. More specifically, the printer is controlled such that it discharges an ink droplet at timing 313 in the backward scan, that is the timing at which a predetermined delay time (delay) 312 is added to the one previous timing 311, instead of the timing 307 that corresponds to the discharge position 307 in the forward scan.
However, recently there are further demands for an improved speed and low cost of printers. In order to meet the demands, attempts have been made to perform printing not only in a region where a printhead moves at constant speed but also in a region where a printhead accelerates or decelerates, or to employ a low-cost motor and components thereof.
In the accelerating and decelerating regions, the printhead moving speed changes. Furthermore, employing a low-cost motor and control components causes cockling of the motor in the constant-speed motion region and causes speed variations due to negatively influenced servo precision. As a result, an ink droplet is discharged in a state where the printhead moving speed varies, and the landing position of the ink droplet deviates from a target position.
When the printhead moving speed varies, landing positions in the forward and backward scans can no longer be adjusted by the registration adjustment using a predetermined delay. Therefore, it is necessary to deviate the landing position of the ink droplet by a predetermined distance. In the region where the printhead moving speed varies, mere delaying of the discharge timing by a predetermined time, as has conventionally been done, still generates an ink landing position deviation for a distance corresponding to the speed variations.
The present invention has been proposed to solve the conventional problems, and has as its object to provide an ink-jet printing apparatus capable of performing registration adjustment in reciprocal printing even if printhead moving speed varies.
Another object of the present invention is to provide a print timing setting method for an ink-jet printing apparatus capable of performing registration adjustment in reciprocal printing even if printhead moving speed varies.
According to the present invention, the foregoing object is attained by providing an ink-jet printing apparatus performing printing by reciprocally scanning a carriage, incorporating a printhead, relative to a print medium, comprising: detection means for outputting a detection signal in accordance with a predetermined distance of a movement of the carriage in a carriage scanning direction; timing signal output means for generating a timing signal in correspondence with a period of the detection signal; time interval detection means for timing a time interval of the detection signal; memory means for storing as reciprocal registration adjustment information a ratio between the time interval of the detection signal and a delay time of the timing signal; delay time setting means for obtaining a delay time of the timing signal based on the information read out from the memory means and the time interval of the detection signal when performing printing in a backward scan; delay signal output means for outputting a delay signal, obtained by delaying the timing signal, in accordance with the delay time; and driving means for driving the printhead based on the delay signal.
Furthermore, the foregoing object is attained by providing a print timing setting method for an ink-jet printing apparatus, which performs printing by reciprocally scanning a carriage, incorporating a printhead, relative to a print medium and includes detection means for outputting a detection signal in accordance with a predetermined distance of a carriage movement in a carriage scanning direction, comprising the steps of: generating a timing signal in correspondence with a period of the detection signal; timing a time interval of the detection signal; storing as reciprocal registration adjustment information a ratio between the time interval of the detection signal and a delay time of the timing signal in memory means; obtaining a delay time of the timing signal based on the information read out from the memory means and the time interval of the detection signal when performing printing in a backward scan; outputting a delay signal, obtained by delaying the timing signal, in accordance with the delay time; and driving the printhead based on the delay signal.
In other words, according to the ink-jet printing apparatus proposed by the present invention, which performs printing by reciprocally scanning a carriage incorporating a printhead relative to a print medium and includes detection means for outputting a detection signal in accordance with a predetermined distance of a carriage movement in a carriage scanning direction, a timing signal is generated in correspondence with a period of the detection signal, a time interval of the detection signal is timed, a ratio between the time interval of the detection signal and a delay time of the timing signal is stored in memory means as reciprocal registration adjustment information, a delay time of the timing signal is obtained based on the information read out from the memory means and the time interval of the detection signal when performing printing in a backward scan, a delay signal obtained by delaying the timing signal is outputted in accordance with the delay time, and the printhead is driven based on the delay signal.
According to the foregoing construction, since the ratio between the time interval of an encoder detection period and delay time can be made constant, it is possible to set a long delay time when carriage moving speed is slow, and set a short delay time when the speed is fast. Therefore, the amount of ink deviation, from the point of being discharged by the printhead to the point of landing on a print medium, can be made constant at all times based on a signal outputted from the encoder regardless of the printhead scanning speed.
Therefore, registration adjustment which is not influenced by variations of printhead scanning speed is possible in reciprocal printing.
The ratio between the time interval of the detection signal and the delay time of the timing signal may be set constant regardless of speed.
Preferably, the delay time setting means sets the delay time short when the time interval is short, and sets the delay time long when the time interval is long.
In this case, the delay time setting means obtains the delay time by performing a predetermined calculation on the time interval.
Preferably, the predetermined calculation obtains the delay time d by d=axc3x97A/n (n is an integer), where A is the time interval and a is a predetermined coefficient. Further, n may be a power of 2.
The printhead may be a printhead which discharges ink by utilizing heat energy and comprises a heat energy transducer for generating the heat energy to be applied to ink.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.